[Coco] Audio recording on CoCo

[John Kent]

On 21/11/2011 4:10 PM, Joel Ewy wrote:
>
>>
>> Second question. Is it _possible_ to save music files on the CoCo and 
>> play them back and sound decent?
>> I would like to work on some software/hardware project on the Coco 
>> and have the music play.
>>  Any ideas?
>>
> You'll need a sound digitizer program for the CoCo.  Oblique Triad put 
> one out called Studio Works that may have ended up on some collection 
> of disk images floating around the Internet.  You'll also need to make 
> a cable that connects your audio source to the CoCo's joystick port 
> where it will be sampled.
>
> Another possibility, I think, is to use the 'play' program in OS-9 to 
> play audio files digitized on a modern PC.  The CoCo's built-in 
> hardware will only do monophonic sound at 6 bits of resolution.  If 
> you have an Orchestra 90 cartridge, it can play 8-bit samples in 
> stereo.  Of course the sample size is limited by the memory of the 
> CoCo.  Not sure if 'play' can stream audio off a hard disk.  Not sure 
> Drivewire or floppy disks could keep up with digitized audio.  That's 
> about all I know about it.
>
> JCE
>

You can buy 16 bit stereo codecs fairly cheaply, but they tend to have 
serial interfaces on them.
You'd need some sort of CPLD to interface a 16 bit serial stereo codec 
to a parallel 8 bit bus for a CoCo.
You could perhaps use a 16 bit IDE interface to connect to a 16 bit 
parallel codec interface.
Timing of the sampling would have to be at 44.1 KHz or what ever it was, 
and you would need a interrupt service routine to read or write the 
codec at that speed and use a memory buffer to overcome latency in the 
disk read and write time. You'd have to be careful to disable interrupts 
before reading or write a sample from the memory buffer and then enable 
them again while writing to the IDE storage device. Since IDE disks of 
CF cards tend to have sector buffers they can be interrupted. i.e. they 
don't have to mask interrupts like a floppy disk drive does. If you used 
CF, there would be a sector read or write delay time that you would have 
to smooth out with memory buffering. The CF or IDE hard disk of course 
would occupy your IDE slot ... dang !

You'd need IDE based storage to handle a file the size of a wave file.

John.

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